The present invention relates to photomultiplier tubes. The tubes comprise a photocathode on a transparent window. The photocathode is a thin layer of a photoemissive material deposited on the transparent window.
The detectors used in particle accelerators generally comprise scintillators associated with mosaics of photomultipliers. The photomultipliers have separate dynodes with gains on the order of 10.sup.4 to 10.sup.6.
The sensitivity and hence the energy resolution of these photomultipliers are greatly reduced by the presence of strong magnetic fields which may reach several thousand Gauss. In order to lessen this problem, the photomultipliers are kept away from the immediate proximity of the accelerators. This requires coupling of the photocathodes to the scintillators with light conductors. However, the use of light conductors reduces resolution.
In order to improve the resolution of the detection devices, photoelectric cells are increasingly used instead of photomultipliers. The photoelectric cells are insensitive to the existing strong magnetic fields (that is, under certain angles between the magnetic field and the axes of the cells). However, in contrast to the photomultiplier, the signal must be amplified outside the photoelectric tube. The external amplification which is necessary generates significant noise.